1. Field of the Invention
The present invention relates to pseudolite transmitters, or more specifically, to network of non-cooperative integrated pseudolite/satellite base station transmitters.
2. Discussion of the Prior Art
The Global Positioning System (GPS) is a system of satellite signal transmitters that transmits information from which an observer""s present location and/or the time of observation can be determined. Another satellite-based navigation system is called the Global Orbiting Navigational System (GLONASS), which can operate as an alternative or supplemental system.
The GPS was developed by the United States Department of Defense (DOD) under its NAVSTAR satellite program. A fully operational GPS includes more than 21 Earth orbiting satellites approximately uniformly dispersed around six circular orbits with four satellites each, the orbits being inclined at an angle of 55xc2x0 relative to the equator and being separated from each other by multiples of 60xc2x0 longitude. The orbits have radii of 26,560 kilometers and are approximately circular. The orbits are non-geosynchronous, with 0.5 sidereal day (11.967 hours) orbital time intervals, so that the satellites move with time relative to the Earth below. Generally, four or more GPS satellites will be visible from most points on the Earth""s surface, and can be used to determine an observer""s position anywhere on the Earth""s surface, 24 hours per day. Each satellite carries a cesium or rubidium atomic clock to provide timing information for the signals transmitted by the satellites. An internal clock correction is provided for each satellite clock.
Each GPS satellite continuously transmits two spread spectrum, L-band carrier signals: an L1 signal having a frequency f1=1575.42 MHz (nineteen centimeter carrier wavelength) and an L2 signal having a frequency f2=1227.6 MHz (twenty-four centimeter carrier wavelength). GPS satellites transmit both a C/A code and a P-code. There are a total of 32 pseudo random (PRN) C/A codes, with each satellite generating a different C/A code. The code modulations that produce either a P-code or a C/A code are impressed onto the L1 carrier and the L2 carrier.
The deployment of additional frequencies is being planned by the DOD. More specifically, DOD is exploring several options to maintain, or improve, the performance of civilian applications of GPS without compromising military utilities. Indeed, the civilian community does not have a second frequency. Today, corrections are based upon L2, which is a military frequency, and subject to DOD use and control. The addition of L5 to the GPS constellation on the Block IIF satellites would, at a minimum, assure the civilian community of the existence of reliable dual frequency transmissions.
As a result, a new GPS frequency, L5, is being considered for civil sector uses in order to reserve L2 for military purposes. This new frequency is targeted to provide both carrier phase and C/A-code range information. Two frequencies are proposed for L5; the first being 1207 MHz yielding a 368 MHz separation from L1, and the second being 1309 MHz having a separation of 266 MHz from L1.
The GPS satellite bit stream includes navigational information on the ephemeris of the transmitting GPS satellite (which includes orbital information about the transmitting satellite within next several hours of transmission) and an almanac for all GPS satellites (which includes a less detailed orbital information about all other satellites). The transmitted satellite information also includes parameters providing corrections for ionospheric signal propagation delays (suitable for single frequency receivers) and for an offset time between satellite clock time and true GPS time. The navigational information is transmitted at a rate of 50 Baud.
A second satellite-based navigation system is the Global Orbiting Navigation Satellite System (GLONASS), placed in orbit by the former Soviet Union and now maintained by the Russian Republic. GLONASS uses 24 satellites, distributed approximately uniformly in three orbital planes of eight satellites each. Each orbital plane has a nominal inclination of 64.8xc2x0 relative to the equator, and the three orbital planes are separated from each other by multiples of 120xc2x0 longitude. The GLONASS satellites have circular orbits with a radii of about 25,510 kilometers and a satellite period of revolution of {fraction (8/17)} of a sidereal day (11.26 hours). A GLONASS satellite and a GPS satellite will thus complete 17 and 16 revolutions, respectively, around the Earth every 8 days. The GLONASS system uses two carrier signals L1 and L2 with frequencies of f1=(1.602+9 k/16) GHz and f2=(1.246+7k/16) GHz, where k (=1,2 . . . 24) is the channel or satellite number. These frequencies lie in two bands at 1.597-1.617 GHz (L1) and 1,240-1,260 GHz (L2). The L1 code is modulated by a C/A-code (chip rate=0.511 MHz) and by a P-code (chip rate=5.11 MHz). The L2 code is presently modulated only by the P-code. The GLONASS satellites also transmit navigational data at a rate of 50 Baud. Because the channel frequencies are distinguishable from each other, the P-code is the same, and the C/A-code is the same, for each satellite. The methods for receiving and demodulating the GLONASS signals are similar to the methods used for the GPS signals.
The European Union plans to develop by 2008 the system of navigation and positioning by satellite designed exclusively for civil purposesxe2x80x94the GALILEO system. GALILEO should enable each individual, by way of a small, cheap individual receiver, to know his or her position to within a few meters, with guaranteed continuity of transmission of the signal. The GALILEO project, supported by the European Space Agency, aims to launch a series satellites at around 20 000 km to be monitored by a network of ground control stations, in order to provide world cover. GALILEO system should be integrated into the existing GNSS-Global Navigation Satellite System, comprising at present time GPS and GLONASS satellite systems.
Reference to a Satellite Positioning System or SATPS herein refers to a Global Positioning System, to a Global Orbiting Navigation System, to a GALILEO project, and to any other compatible satellite-based system that provides information by which an observer s position and the time of observation can be determined, all of which meet the requirements of the present invention.
A Satellite Positioning System (SATPS), such as the Global Positioning System (GPS) or the Global Orbiting Navigation Satellite System (GLONASS), uses transmission of coded radio signals, with the structure described above, from a plurality of Earth-orbiting satellites. A SATPS antenna receives SATPS signals from a plurality (preferably four or more) of SATPS satellites and passes these signals to an SATPS signal receiver/processor, which (1) identifies the SATPS satellite source for each SATPS signal, (2) determines the time at which each identified SATPS signal arrives at the antenna, and (3) determines the present location of the SATPS satellites.
The range (ri) between the location of the i-th SATPS satellite and the SATPS receiver is equal to the speed of light c times (xcex94ti), wherein (xcex94ti) is the time difference between the SATPS receiver""s clock and the time indicated by the satellite when it transmitted the relevant phase. However, the SATPS receiver has an inexpensive quartz clock which is not synchronized with respect to the much more stable and precise atomic clocks carried on board the satellites. Consequently, the SATPS receiver estimates a pseudo-range (pri) (not a true range) to each satellite.
After the SATPS receiver determines the coordinates of the i-th SATPS satellite by demodulating the transmitted ephemeris parameters, the SATPS receiver can obtain the solution of the set of the simultaneous equations for its unknown coordinates (x0, y0, z0) and for unknown time bias error (cb). The SATPS receiver can also determine velocity of a moving platform.
The given below discussion, (applicable to any satellite navigational system, but focused on GPS applications to be substantially specific) can be found in xe2x80x9cGlobal Positioning System: Theory and Applicationsxe2x80x9d, Volume II, Chapters 1 and 5, by Bradford W. Parkinson and James J. Spilker Jr., published by the American Institute of Aeronautics and Astronautics, Inc. in 1996.
Typically, GPS based positions are calculated using the World Geodetic System of 1984 (WGS84) coordinate system. These positions are expressed in Earth Centered Earth Fixed (ECEF) coordinates of X, Y, and Z axes. These positions are often transformed into latitude, longitude, and height relative to the WGS84 ellipsoid.
Differential Global Positioning System (DGPS) is a technique that significantly improves both the accuracy and the integrity of the Global Positioning System (GPS). The most common version of DGPS requires high-quality GPS xe2x80x9creference receiversxe2x80x9d at known, surveyed locations. The reference station estimates the slowly varying error components of each satellite range measurement and forms a correction for each GPS satellite in view. This correction is broadcast to all DGPS users on a convenient communication link. Typical ranges for a local area differential GPS (LADGPS) station are up to 150 km. Within this operating range, the differential correction greatly improves accuracy for all users, regardless of whether selective availability (SA) is activated or is not. This improvement in the accuracy of the Global Positioning System (GPS) is possible because the largest GPS errors vary slowly with time and are strongly correlated over distance. DGPS also significantly improves the xe2x80x9cintegrityxe2x80x9d of GPS for all classes of users, because it reduces the probability that a GPS user would suffer from an unacceptable position error attributable to an undetected system fault. Expected accuracies with DGPS are within the range from 1 to 5 meters.
Most DGPS systems use a single reference station to develop a scalar correction to the code-phase measurement. If the correction is delivered within 10 seconds, and the user is within 1000 km, the user accuracy should be between 1 and 10 meters. Users with very stringent accuracy requirements may be able to use a technique called carrier-phase DGPS or CDPGS. These users measure the phase of the GPS carrier relative to the carrier phase at a reference site; thus achieving range measurement precision that is a few percent of the carrier wavelength, typically about one centimeter. These GPS phase comparisons are used for vehicle attitude determination and also in survey applications, where the antennas are separated by tens of kilometers. If the antennas are fixed, then the survey is called static, and millimeter accuracies are possible, because long averaging times can be used to combat random noise. If the antennas are moving, then the survey is kinematic, and shorter time constants should be used with some degradation of accuracy.
Pseudolites (PLs) are ground-based transmitters that can be configured to emit GPS-like signals for enhancing the GPS by providing increased accuracy, integrity, and availability. Accuracy improvement can occur because of better local geometry, as measured by a lower vertical dilution of precision (VDOP). Availability is increased because a PL provides an additional ranging source to augment the GPS constellation.
However, a potential user of PL ranging signals should address the xe2x80x9cnear-farxe2x80x9d problem associated with the PL signal level. One solution to the near-far problem is to configure a set of pseudolites operating within the GPS frequency bands (L1: 1565-1585 MHz or L2: 1217-1237 MHz) to serve a limited area with a power level low enough to preclude appreciable interference to standard GPS signals. Another solution to the near-far problem is to design the PL signal configuration to operate within L1 band and mitigate or virtually eliminate the near-far issue.
The copending patent application entitled xe2x80x9cINTEGRATED PSEUDOLITE/SATELLITE BASE STATION TRANSMITTERxe2x80x9d by the inventor Charles R. Trimble is filed on the same date as the current patent application, is assigned to the same entity, is referred to in the current patent application as the patent application #1, and is incorporated in the current patent application in its entirety.
The patent application #1 discloses a pseudolite transmitter (PL) integrated with a satellite base station (SBS), wherein the pseudolite transmitter (PL) includes a designed signal configuration that allows a user to operate within L1 band and to mitigate or virtually eliminate the near-far issue, and wherein the SBS allows to lock the timing of the pseudolite (PL) transmitter to the satellite time, and to provide an automatic determination of the location of the integrated PL/SBS transmitter.
Let us assume that a first plurality of K integrated PL/SBS transmitters owned by the first entity (in conjunction with a plurality of visible satellite signals) provides a substantially sufficient coverage of an open area A, so that a first mobile navigation/positioning receiver located in the open area A receives a substantially sufficient number of ranging signals for its navigation/positioning purposes including a plurality of K ranging signals from the network of K integrated PL/SBS transmitters, wherein K is an integer.
Let us further assume that a second entity owns a second plurality of M integrated PL/SBS transmitters and also would like to place a second mobile navigation/positioning receiver in the area B that overlaps with the area A. However, the second entity would like to use the ranging signals provided by the first plurality of K integrated PL/SBS transmitters owned by the first entity in the overlapping area of coverage before using its own plurality of M integrated PL/SBS transmitters, so that the second plurality of M integrated PL/SBS transmitters initially stays idle in order not to interfere with the first plurality of integrated PL/SBS transmitters. Thus, the second entity need not to ask or apply for license from the first entity to use its transmitters. However, if the second mobile navigation/positioning receiver navigates to the area B, wherein the ranging signals generated by the first plurality of K integrated PL/SBS transmitters do not penetrate, the second plurality of M integrated PL/SBS transmitters becomes active and provides the necessary coverage for the second mobile navigation/positioning receiver without interfering with the signals generated by the first plurality owned by the first entity. This is a non-cooperative use by the second entity of ranging signals generated by the first entity.
What is needed is to disclose the interaction between the sub-networks of non-cooperative transmitters owned by the first and the second non-cooperative entities.
To address the shortcomings of the available art, the present invention discloses the sub-networks of non-cooperative transmitters owned by the first and the second non-cooperative entities, and methods of interaction between the sub-networks of non-cooperative transmitters owned by the first and the second non-cooperative entities.
One aspect of the present invention is directed to a network of non-cooperative integrated pseudolite (PL)/satellite base station transmitters covering an open area. In one embodiment, the network comprises: a first plurality (K) of integrated pseudolite/satellite base station (PL)1/(SBS) transmitters located in an open area A, and a second plurality (M) of non-cooperative integrated PL2/SBS transmitters located in an open area B, wherein K and M are integers. Each PL1 or PL2 transmitter is co-located with one SBS, and has a predetermined duty cycle. At least one SBS provides a satellite timing synchronization signal. Each integrated active (transmitting) PL1/SBS transmitter transmits its position location as a part of its message.
In one embodiment, the first plurality (K) of integrated PL1/SBS transmitters includes a substantially sufficient number K1 of active integrated PL1/SBS transmitters in order to fill out satellite shades of coverage and to substantially cover the area A so that a first mobile navigation/positioning receiver located in the area A receives a substantially sufficient number of ranging signals for its navigation/positioning purposes including K1 ranging signals from the first plurality of PL1/SBS transmitters, wherein K1 is an integer less or equal to K.
In one embodiment, each integrated PL2/SBS transmitter continuously detects a plurality (K2) of ranging signals transmitted by each active integrated PL1/SBS transmitter. In this embodiment, each integrated PL2/SBS transmitter includes a processor including an algorithm comprising at least the following logic: (a) each integrated PL2/SBS transmitter does not transmit if the plurality (K2) of active integrated PL1/SBS transmitters substantially covers the area B so that a second mobile navigation/positioning receiver located in the area B receives substantially sufficient number of ranging signals for its navigation/positioning purposes including K2 ranging signals from the first plurality of non-cooperative integrated PL1/SBS transmitters; (b) at least a plurality (M1) of integrated PL2/SBS transmitters starts transmitting, if a plurality (K3) of integrated PL1/SBS transmitters does not substantially cover the open area B, so that the second mobile navigation/positioning receiver located in the area B receives substantially sufficient number of ranging signals for its navigation/positioning purposes including M1 ranging signals from the second plurality of non-cooperative PL2/SBS transmitters and including K3 ranging signals from the first plurality of non-cooperative integrated PL1/SBS transmitters. Herein, M1 is an integer less or equal to M, K2 is an integer less or equal to K1, and K3 is an integer less or equal to K1.
Another aspect of the present invention is directed to a network of non-cooperative pseudolite (PL) transmitters covering an in-door area comprising an area A and an area B. In one embodiment, the network comprises a first plurality (K) of pseudolite (PL)1 transmitters, located in an in-door area A, and a second plurality (M) of non-cooperative pseudolite (PL)2 transmitters, located in an in-door area B, wherein K and M are integers. Each pseudolite (PL)1 ((PL)2) transmitter is locked to a satellite time and has a predetermined duty cycle.
In one embodiment, the first plurality (K) of pseudolite (PL)1 transmitters includes a substantially sufficient number K1 of active (transmitting) pseudolite (PL)1 transmitters in order to substantially cover the in-door area A so that a first mobile navigation/positioning receiver located in the in-door area A receives a substantially sufficient number of ranging signals for its navigation/positioning purposes including K1 ranging signals from the first plurality of PL1 transmitters, wherein K1 is an integer less or equal to K.
In one embodiment, each pseudolite (PL)2 transmitter continuously detects at least one ranging signal transmitted by at least one pseudolite PL transmitter. In this embodiment, each pseudolite (PL)2 transmitter includes a processor including an algorithm comprising at least the following logic: (a) the pseudolite (PL)2 transmitter does not transmit if the plurality (K2) of pseudolite (PL)1 transmitters substantially covers the area B so that a second mobile navigation/positioning receiver located in the area B receives substantially sufficient number of ranging signals for its navigation/positioning purposes including the K2 ranging signals from the first plurality of pseudolite (PL)1 transmitters; (b) at least a plurality (M1) of pseudolite (PL)2 transmitters starts transmitting, if a plurality (K3) of pseudolite (PL)1 transmitters does not substantially cover the in-door area B, so that a second mobile navigation/positioning receiver located in the area B receives substantially sufficient number of ranging signals for its navigation/positioning purposes, including M1 ranging signals from the second plurality of non-cooperative pseudolite (PL)2 transmitters and including K3 ranging signals from the first plurality of non-cooperative pseudolite (PL)1 transmitters. Herein, K2 is an integer less or equal to K1, K3 is an integer less or equal to K1, and M1 is an integer less or equal to M.
One more aspect of the present invention is directed to a network of non-cooperative integrated pseudolite (PL)1/SBS transmitters and non-cooperative pseudolite (PL)2 transmitters covering an area comprising an open area A and an in-door area B.
In one embodiment, the network comprises: a first plurality (K) of integrated (PL)1/SBS transmitters, located in the open area A, and a second plurality (M) of non-cooperative pseudolite (PL)2 transmitters, located in an in-door area B. K is an integer, and M is an integer. Each PL1 transmitter is co-located with one SBS. Each SBS provides a satellite timing synchronization signal to at least one PL1 transmitter; wherein each pseudolite (PL)2 transmitter is locked to a satellite time. Each PL1 has a predetermined duty cycle.
In one embodiment, the first (K) plurality of integrated (PL)1/SBS transmitters includes a substantially sufficient number K1 of transmitting (active) integrated (PL)1/SBS transmitters in order to fill out satellite shades of coverage and to substantially cover the area A. Each integrated (PL)1/SBS transmitter transmits its position location as a part of its message in order to provide the substantially sufficient number K1 of ranging signals to a first mobile navigation/positioning receiver located in the area A for its navigation/positioning purposes. K1 is an integer less or equal to K.
In one embodiment, each (PL)2 transmitter continuously detects a plurality (K2) of ranging signals transmitted by a plurality (K2) of integrated (PL)1/SBS transmitters. In this embodiment, each (PL)2 transmitter includes a processor including an algorithm comprising at least the following logic: (a) each (PL)2 transmitter does not transmit if the plurality (K2) of integrated (PL)1/SBS transmitters substantially covers the area B so that a second mobile navigation/positioning receiver located in the area B receives substantially sufficient number of ranging signals K2 from the first plurality of integrated (PL)1/SBS transmitters for its navigation/positioning purposes; (b) at least a plurality (M1) of (PL)2 transmitters starts transmitting, if a plurality (K3) of integrated (PL)1/SBS transmitters does not substantially cover the in-door area B, so that a second mobile navigation/positioning receiver located in the area B receives substantially sufficient number of ranging signals for its navigation/positioning purposes, including M1 ranging signals from the second plurality of non-cooperative (PL)2 transmitters and including K3 ranging signals from the first plurality of non-cooperative integrated (PL)1/SBS transmitters.
Herein, K2 is an integer less or equal to K1, K3 is an integer less or equal to K1, and M1 is an integer less or equal to M.
An additional aspect of the present invention is directed to a method for using a network of non-cooperative integrated pseudolite (PL)/satellite base station transmitters and non-cooperative pseudolite (PL) transmitters to cover an area comprising an open area A and an in-door area B. The network comprises a first plurality (K) of integrated pseudolite (PL)1/SBS transmitters located in an open area A, and a second plurality (M) of non-cooperative M pseudolite (PL)2 transmitters located in an in-door area B; wherein K and M are integers.
In one embodiment, the method comprises the following steps: (a) locking each (PL)1 transmitter to a satellite time; (b) providing a substantially sufficient number M1 of ranging signals to a second mobile navigation/positioning receiver located in the area B for its navigation/positioning purposes; wherein each (PL)2 transmitter transmits its position location as a part of its message; (c) providing a satellite timing synchronization signal to each integrated (PL)1/SBS transmitter; (d) continuously detecting a plurality M2 of ranging signals transmitted by a plurality M2 of (PL)2 transmitters by each integrated (PL)1/SBS transmitter; (e) starting transmitting by at least K1 number of integrated (PL)1/SBS transmitters, if the plurality M2 of ranging signals transmitted by the plurality M2 of (PL)2 transmitters does not substantially cover the out-door area A; and (f) providing a substantially sufficient number of ranging signals to a first mobile navigation/positioning receiver located in the area A for its navigation/positioning purposes, including M2 ranging signals from the second plurality of non-cooperative (PL)2 transmitters and including K1 ranging signals from the first plurality of non-cooperative integrated (PL)1/SBS transmitters. M1 is an integer less or equal to M, M2 is an integer less or equal to M1, and K1 is an integer less or equal to K.